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Cloud-Feeding Aerosols May Be Why Storms Are Getting More Extreme

They can make clouds grow larger and live longer.

Aerosols — the tiny particles in the atmosphere that come from natural sources such as volcanic eruptions and desert dust, or human-made sources including the burning of wood, coal, and oil — often form the nucleus of cloud droplets around which water condenses. Without these aerosols, there would be far fewer clouds in the sky.

According to a new study that will be published in the journal Proceedings of the National Academy of Sciences, aerosols in the atmosphere can also increase the lifespan of large storm clouds by delaying rainfall, making the clouds grow larger and live longer, and producing more extreme storms.

The study is the first confirmation of the hypothesis that aerosol particles have a lasting effect on the life cycle of large thunderstorm systems called mesoscale convective systems (MSC).

An MSC is an extremely complex collection of thunderstorms that act as one system. They are often violent, and can spread across an entire state and last for more than 12 hours. According to the paper, these systems are the "primary source of precipitation over the tropics and mid-latitudes, and their lifetime can have a large influence on the variability of rainfall, especially extreme rainfall that causes flooding."

To evaluate the role of aerosols in these systems, the research team, led by scientists from the University of Texas (UT) at Austin Jackson School of Geosciences, looked at data from two different types of satellites — MODIS and geostationary. After analyzing the data and observations from 2,430 convective cloud systems, the team found that aerosols can help increase their lifespans by as much as 3 to 24 hours, depending on regional meteorological conditions. This means that the storms can dump a lot more water onto a region.

"A cloud particle is basically water and aerosols. It's like a cell. The aerosol is the nucleus and the water is the cytoplasm," said lead author Sudip Chakraborty in a UT news release. "The more aerosols you have, the more cells you get. And if you have more water, you should get more rain."

Although meteorological conditions, such as relative humidity, available convective energy, and wind shear, are still the most important element in determining the lifespan of an MCS, aerosols still have an important role, explained Rong Fu, a professor in the Jackson School Department of Geological Sciences and co-author of the study.

In fact, how aerosols affect convective clouds and the climate system is something researchers have been studying for more than 10 years. According to Professor Daniel Rosenfeld of the Hebrew University of Jerusalem, one of the world's leading researchers in the field and who was not involved in the study, the results have significantly advanced the science.

"This is the first study that shows the full life cycle of convective clouds in a statistically meaningful way on a climate scale," concluded Rosenfeld.